Water— The Elixir of Life!

Why are we studying water? All life occurs in water Inside & outside the cell Based on work by K. Foglia www.kimunity.com

Chemistry of Water Water is a polar molecule Polar covalent bonds Unequal sharing of the electrons Based on work by K. Foglia www.kimunity.com

Chemistry of Water H2O molecules form H bonds with each other + attracted to – creates a sticky molecule Based on work by K. Foglia www.kimunity.com

Cohesion H bonding between H2O creates cohesion water is “sticky” surface tension drinking straw can you suck sugar up a straw? Based on work by K. Foglia www.kimunity.com

Adhesion H2O molecules form H bonds with other substances Capillary action Meniscus Water climbs up fiber ex. paper towel Based on work by K. Foglia www.kimunity.com

How does H2O get to the top of a tree? Transpiration Show video here! Based on work by K. Foglia www.kimunity.com

Water is the solvent of life H2O is a good solvent due to its polarity polar H2O molecules surround + & – ions solvents dissolve solutes creating aqueous solutions What dissolves in water easily? polar or non-polar molecules? How about Oxygen? Does that dissolve in H2O? Based on work by K. Foglia www.kimunity.com

Solutes and Solutions Mixture: material composed of two or more elements or compounds 2 types: Solutions and Suspensions Solution: Components are evenly distributed Ex. Sodium chloride breaks apart in water Solute- substance that is dissolved Solvent- the substance in which the solute dissolves Based on work by K. Foglia www.kimunity.com

B. Suspension- mixtures that have materials that do not dissolve in water Ex. sand in water Based on work by K. Foglia www.kimunity.com

Hydrophilic Hydrophilic Substances have affinity for H2O Polar Ionic What dissolves in water easily? polar or non-polar molecules? How about Oxygen? Does that dissolve in H2O? Based on work by K. Foglia www.kimunity.com

Hydrophobic Hydrophobic substances do not have affinity for H2O non-polar non-ionic What dissolves in water easily? polar or non-polar molecules? How about Oxygen? Does that dissolve in H2O? fat (triglycerol) Based on work by K. Foglia www.kimunity.com

The Special Case of Ice Most (all?) substances are more dense when they are solid But not water… Ice floats! H bonds form a crystal with loose structure Based on work by K. Foglia www.kimunity.com

Ice floats Based on work by K. Foglia www.kimunity.com

Why is “ice floats” important? Oceans & lakes don’t freeze solid If ice sank… Eventually all ponds, lakes & even ocean would freeze solid During summer, only upper few inches would thaw Surface ice insulates water below Allowing life to survive the winter Seasonal turnover of lakes Cycling nutrients Based on work by K. Foglia www.kimunity.com

Specific heat H2O has high specific heat due to H bonding H2O resists changes in temperature takes a lot to heat it up takes a lot to cool it down H2O moderates temperatures on Earth Based on work by K. Foglia www.kimunity.com

Evaporative Cooling Organisms rely on heat of vaporization to remove heat Based on work by K. Foglia www.kimunity.com

Punch-line Water is a polar molecule The special properties of water make life on Earth possible The chemical behavior of water governs how organisms function Based on work by K. Foglia www.kimunity.com